JPS5850178A - One side narrow groove welding method of increased welding speed - Google Patents

Abstract

PURPOSE:To make the formation of a superior welded joint by high speed welding possible in the stage of one side welding of members to be welded having a narrow groove by decreasing a welding heat input and performing MIG welding from the initial layer without burn-through and formation of recesses. CONSTITUTION:In the stage of butt welding of thick walled pipes 1, 2, an initial layer is formed round the pipes along a narrow groove 3. Here, in the beginning end part of the initial layer, a root face 5 is melted and solidified beforehand to form a welded layer 6 for the beginning end part by MIG welding. The 1st layer is welded by MIG welding of about 12,000-17,000J/cm welding heat input to form a weld zone 12 of good quality quickly. In succession the welding from the 2nd layer up to excess metal is accomplished by MIG welding at about >=17,000J/cm welding heat input. According to this method, the welded joint part of high quality is formed in the narrow groove in the shorter time than by the prior art which forms the 2nd layer by TIG welding.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a single-sided narrow gap welding method, and particularly to a welding method that can achieve a high welding speed and form a good welded joint.

Recently, there has been an increasing need for welding thick, large-diameter pipes, and welding pipes and end plates, but since double-sided welding is difficult or impossible for these welding processes, single-sided welding is used. . In addition, from the viewpoint of the reliability of the welded part and the economic efficiency of welding work, it was desirable to use a narrow gap, and the inventors first filed a patent application in 1983.
-21 etc., provided a narrow gap single-sided welding method.

When welding a workpiece with a narrow gap from one side, this method uses T-G (tungsten inert gas arc) welding for the first and second layers to form a good and uniform back wave, and to weld the third layer. After that, the welding speed was increased by M-G (metal arc inert gas) welding up to the excess welding.
In addition, by forming the first layer and the second layer by T welding and G welding, melting through and deformation of the back wave due to MIG welding can be prevented. This method skillfully combines the formation of uniform back waves by TUG welding and the speeding up of welding work by M-G1 valley welding, but the first and second layers are welded at a slower welding speed than T-G. Since the process involves welding, there is a demand for even faster work. In addition, it is not practical to use M/G welding from the first layer because the melting will drop and dents will occur due to the melting of the back waves.

SUMMARY OF THE INVENTION An object of the present invention is to provide a single-sided narrow gap welding method that eliminates the above-mentioned problems, increases welding speed, and provides a good welded joint.

In short, this invention reduces the welding heat input compared to the conventional M"G welding, and as a result, the melt drops and MIG welding is performed from the first layer without forming dents, etc., without degrading the quality of the welded joint. An object of the present invention is to provide a single-sided narrow gap welding method that increases welding speed.

This invention will be explained in detail below.

First, the thermal energy of the welding arc can be approximately considered to be the value obtained by converting the hypocardial input into thermal energy, and is given by the following equation.

Q: = 0.24V (1) However, -%Q is the thermal energy (
ca's), v is the welding arc voltage.

is the arc current (A).

What is the moving speed of the arc, that is, the welding speed? (am
/min), welding heat input (heat amount per unit length of welding) H(J/am) is given by the following formula.

H-□・Mountain...(2) In formula (2), the welding heat input H is generally about 17oooJ/cm and is called standard welding conditions. Specifically, for example, welding current: 17OA, welding voltage: 25V, and melting speed: 15cm/min.

Figure 1 shows a single-sided narrow gap welding method for thick-walled pipe 1;
The figure shows the mating state of this pipe 1 and another pipe 2 at A- in Fig. 1.
It is shown along line A. However, the tube 2 is not shown in FIG. Reference numeral 3 indicates a narrow gap, 4 indicates a root gap, and 5 indicates a root face. The welding method is to circumnavigate the tube 1 along the narrow tip 3 to form the first layer. In this case, the starting end of the first layer is melted and solidified by T welding the root face 5 as shown in Fig. 4. , it is preferable to form a starting edge welding layer 6. This is because when performing 'MIG welding from the initial layer as described later, the welding of the initial layer is completed and the next layer, that is, the second layer is formed at the starting edge.
This is to prevent welding heat from being absorbed by the already welded metal when forming the layer, resulting in local penetration failure.

Next, we will show how to weld the first layer. If M/G welding is performed from the first layer using the conventional method, the melting will drop as described above, and problems such as the formation of recesses will occur. Here, as a result of various welding experiments, the inventors found that under the conditions shown below, M-G from the first layer
It was confirmed that no welding defects occurred even when welding was performed.

<Welding conditions> Welding current: 180 to 200 A Welding voltage: 27 to 29 V Welding speed: 20 to 24 If the above conditions are substituted into equation (2) to find the welding heat input H, H is at least 1
From 2150 J/cm to a maximum of 17400 J/am *Tonago. However, in the vicinity of 17,000 J/cm, there are problems such as a drop in melting, and on the contrary, in the vicinity of 1'200' OJ/cm, there is a risk of poor penetration. Although the conditions vary somewhat depending on the materials used, wall thickness, etc., good results were obtained with approximately 15,000J10m≠.

That is, for the first layer, M/G welding is performed with a welding heat input H of approximately 15oooJ/cm. FIG. 3 shows the state in which this M welding is being performed, in which a wire (welding wire rod) 11 bent into a corrugated shape advances through a passage 10 inside the nozzle 9 inserted into the narrow gap 3, and the wire After exiting the nozzle opening, the end of the weld 11 swings left and right as shown by the arrow with respect to the direction of welding progress, forming a stable arc and rapidly forming a high-quality weld 12. In addition, in the case of T-work G welding in Fig. 4, this nozzle /l/
By inserting the 10 L tungsten electrode 13, the starting end welding layer 6 can be formed using the same welding equipment as the M-G welding.

Since the first layer M welding 12 can form an initial layer thickness t that can sufficiently withstand the welding heat of normal M welding, we perform M welding G welding under normal conditions from the second layer onwards. In other words, from the second layer onwards, the welding heat input H is set to about 17oooy7m or more to perform more efficient welding. As a result, it was confirmed that the welding time for the first layer can be shortened to approximately T when compared with the conventional method of performing the first and second layers by T welding and G welding.

By implementing the present invention, the working time for single-sided narrow gap welding can be significantly shortened, and a high-quality welded joint can be formed.

[Brief explanation of the drawing]

Figure 1 is a front view of one of the tubes showing the welding surfaces of the two tubes to be welded, Figure 2 is a cross-sectional view taken along line A-A in Figure 1, and Figure 3 is line-B-B in Figure 1. A sectional view, FIG. 4 is a sectional view taken along line BB in FIG. 1, showing the method of T-work G welding.

Claims (1)

[Claims] 1. In a method of welding a member to be welded having a narrow gap from one side, the welding heat input of the first layer is approximately 1200QJ/c.
Single-sided narrow gap welding with increased welding speed, characterized by M G welding from m to about 17oooy/cm, and MUG welding with welding heat input of about 17000 J/cm or more from the second layer to the overfill. Method. 2. TI the root face of the starting end of the first layer M work G welding
A single-sided narrow gap welding method with increased welding speed as claimed in claim 1, characterized in that the starting end weld layer is formed by melting and solidifying by G welding. 3. The welding heat input for first layer M welding is approximately 15,000 J/C.
A single-sided narrow gap welding method with increased welding speed according to claim 1 or 2, characterized in that the welding speed is set to m.